Low-intensity lifestyle interventions during pregnancy can prevent excessive gestational weight gain in normal weight women. However, preventing excessive gestational weight gain in obese women has proven more difficult. Intensive interventions involving prescription of specific calorie goals and balanced nutrition have shown the most promise, but, similar to non-pregnant populations, promoting ongoing adherence to caloric prescription remains a significant challenge. Liquid meal-replacement products have been shown to promote adherence to calorie and weight goals in non-pregnant multiethnic populations. Moreover, they have been used during pregnancy as a supplement to improve nutritional adequacy and shown to be safe and to result in improved dietary intal<e. However, no study to date has evaluated this approach as a means to prevent excessive weight gain during pregnancy. The principal aim of this study is to determine whether a multi-component lifestyle intervention that incorporates partial meal replacements during pregnancy can reduce the number of obese women who exceed the lOM recommendations for weight gain during pregnancy. In this two-site randomized trial, 430 obese women, 50% Hispanic, will be randomized within site and ethnicity into either a multi-component lifestyle modification treatment with partial meal replacement program (N=215) or standard care (N=215). Treatment will occur during pregnancy, using standardized intervention procedures from our previous work. All women will be recruited and assessed early in pregnancy (between 10 and 16 weelis), at 30 weeks gestation, and at 6 months, and 12 months postpartum with anthropometric measures obtained at delivery and at 2 months postpartum. We believe this project is significant because it deals with the prevention of excessive gestational weight gain and its associated adverse maternal and offspring health consequences. The study is also innovative; there have been no randomized controlled trials evaluating the effects of a behavioral lifestyle intervention with partial meal replacement program to promote healthy weight gain in multiethnic obese women.